Which of the following choices represents the material that may not be exposed to certain types of light?

The correct choice pertains to PEX, which stands for cross-linked polyethylene. PEX has specific limitations when it comes to exposure to ultraviolet (UV) light. When exposed to UV light, PEX can degrade and become brittle over time, which can lead to failure in plumbing systems. This unease is particularly concerning for PEX tubing intended for outdoor use or where it might be exposed to sunlight. Consequently, appropriate measures must be taken to protect PEX from UV exposure, such as burying it underground or covering it with insulation.

In contrast, the other materials listed—PVC, ABS, and CPVC—are generally more resistant to UV light. While all plastic materials can degrade over extended periods of exposure to sunlight, PVC and CPVC are typically used in applications that may involve UV light exposure without immediate concern for degradation. ABS, while not recommended for prolonged UV exposure either, doesn’t inherently degrade as quickly as PEX. Understanding these properties is essential for selecting appropriate plumbing materials in various installations.